1. Field of the Invention
This invention relates to a process for the production of high purity silicon by arc heater reduction of silicon intermediates.
2. Description of the Prior Art
The commercial development of electric power generation based on silicon photovoltaic devices requires a substantial decrease in the production costs of high purity silicon as well as an increase in production capacity thereof. Heretofore the overall process in the production of high purity silicon consisted of four steps including (1) reduction of silica with carbon to produce metallurgical grade silicon, (2) conversion of metallurgical grade silicon to one or more intermediate compounds such as trichlorosilane by reaction with a hydrogen halide such as hydrogen chloride, (3) purification of the intermediate compounds, and (4) decomposition of the intermediate compounds to polycrystalline silicon. The final step (4) in the process is carried out in a reactor containing resistance heated silicon rods in which hydrogen and the intermediate compounds are introduced. The intermediate compounds react with the hydrogen, producing polycrystalline silicon which is deposited on the resistance heated rods. This step is very inefficient since it must be carried out at temperatures below the melting point of silicon, which results in a low yield of silicon. At higher temperatures, the halosilanes, i.e., the fluorosilanes, chlorosilanes, and iodosilanes, become much less stable and thus a higher process yield would result. Furthermore, the prior art decomposition step is a batch process in which the reactor must be shut down and opened to remove the deposited silicon which causes a decrease in the overall production rate for a given installation period.